1. Field of the Invention
The present invention relates to a control apparatus of an internal combustion engine which properly controls the timing of the first fuel injection for engine starting to improve engine startability.
2. Description of the Related Art
Conventionally, an in-cylinder injection type of internal combustion engine has widely been used, in which fuel is injected not to an air-intake port but directly to a combustion chamber. In this in-cylinder injection type of internal combustion engine, air is drawn into the combustion chamber through the air-intake port when an air-intake valve is opened, and the air is compressed as a piston moves up. Then fuel is injected directly to the intake air or the compressed high-pressure air through a fuel injection valve. Consequently, the high-pressure air and the misty fuel are mixed in the combustion chamber. The air-fuel mixture is exploded by spark plug ignition, and the exhaust gas exits through the air-intake port when an exhaust valve is opened.
In this in-cylinder injection type of internal combustion engine, a fuel combustion condition is controlled by changing fuel injection timing depending on an operation status of the internal combustion engine. Specifically, when the internal combustion engine is in low load conditions, fuel is injected into the high-pressure air in the compression stroke to form the air-fuel mixture within a limited area in the combustion chamber. The high-pressured air-fuel mixture is ignited by the spark plug, resulting in stratified combustion. When the internal combustion engine is in middle or high load conditions, fuel is injected into the intake air in the intake stroke to form the air-fuel mixture which disperses in all over the combustion chamber. The air-fuel mixture dispersing in the combustion chamber, which is compressed, is ignited by the spark plug, resulting in homogeneous combustion.
Such an in-cylinder injection type of internal combustion engine requires high-pressure fuel to atomize the injected fuel in addition to the high-pressure air when fuel injection is performed in the compression stroke. This is because the time period from the injection to combustion is short. For this reason, the fuel in a fuel tank is pressured by using a high-pressure pump to feed the high-pressure fuel to an injector. This type of internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) No. H11-270385.
In the internal combustion engine described in JP-A No. H11-270385, fuel pumped from a fuel tank by a low-pressure pump is made high-pressure by a high-pressure pump to feed to a fuel injection valve. In-cylinder fuel injection is not allowed until the fuel pressure exceeds a predetermined level at an early stage of engine starting, and in the meanwhile, the fuel pressure is immediately increased, so that engine startability is improved with prompt atomization of the injected fuel from the beginning of the injection.
However, in the in-cylinder injection type of internal combustion engine, even when the fuel pressure injected through the fuel injection valve is high, fluctuations in temperature or pressure inside the combustion chamber combustion would cause fluctuations in atomization of the fuel to be injected from the fuel injection valve, thereby not keeping combustion stable. In this case, internal combustion engines having the same system may have manufacturing or assembling tolerances and assembling variations, which may cause fluctuations in temperature or pressure inside the combustion chamber depending on the individual internal combustion engine. Hence, only controlling the fuel pressure makes it difficult to keep the combustion state stable with uniform atomization of the injected fuel.